We will measure quantitative scattering parameters for biological tissues. These data will be useful to improve utility of diagnostic procedures using reflected or scattered ultrasound in two ways. First, knowledge of the factors which govern the strength of the observed echoes will be useful in the design of clinical apparatus. Second, knowledge of scattering parameters will be useful in differential diagnosis and the identification of particular tissues if the scattered echoes are found to characterize particular tissues. We will extend the methods already used by us to measure scattering parameters of blood to new investigations of blood and of solid tissues. Methods have been derived by us to measure backscattering cross-sections corrected for absorption and measurement equipment parameters. Scattering from blood has been quantitated and compared with a theoretical model as a function of frequency and concentration over the usually encountered ranges. Extension of these measurements to higher hematocrits, varying flow velocities and to solid tissues is now underway. The absolute scattering parameters of solid tissues will be measured first in vitro as functions of frequency and angle. Spectral analysis of the input, transmitted, and scattered signals will be employed to help determine a suitable scattering model. These models will then be used to reduce the data for comparison with physical quantities, i.e., density, compressibility which characterize the tissue. Tissues to be measured include muscle, myocardium, endocardium, heart valves, blood vessel walls, and plaque as well as blood.